Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $56.75   8.573%   $61.6152   $61.62   $61.60   $61.60  
  Purchase #2 $223.34   12.268%   $250.7394   $250.74   $250.75   $250.70  
  Purchase #3 $165.52   7.728%   $178.3114   $178.31   $178.30   $178.30  
  Purchase #4 $33.71   12.159%   $37.8088   $37.81   $37.80   $37.80  
  Purchase #5 $82.81   6.626%   $88.297   $88.30   $88.30   $88.30  
  Purchase #6 $102.70   11.711%   $114.7272   $114.73   $114.75   $114.70  
  Purchase #7 $195.74   4.748%   $205.0337   $205.03   $205.05   $205.00  
  7 purchase totals = $860.57       $936.5327   $936.54   $936.55   $936.40